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We evaluated the mechanisms of histamine-mediated adenylate cyclase stimulation in 18 human hearts obtained from cardiac transplant recipients or prospective donors. Mg2+ and guanyl nucleotide were required for histamine stimulation. In the presence of 10-5 M GTP, histamine produced a maximal stimulation of 1.54 +/- 0.06 times basal activity in left ventricle (39% of the isoproterenol maximum), which rose to 1.75 +/- 0.14 times basal activity (68% of the isoproterenol maximum) in the presence of a 10-5M concentration of the synthetic guanyl nucleotide 5'-guanylyl imidodiphosphate. Histamine stimulation of adenylate cyclase was antagonized by cimetidine (KB = 1.58 X 10-6 M) but not by H1-blocking doses of mepyramine or pyrrobutamine. The selective H2 agonist dimaprit stimulated adenylate cyclase to approximately the same extent as histamine, whereas a selective H1 agonist produced only minimal stimulation that was H2-mediated. The selective H2 agonist impromidine was a partial agonist and produced approximately 20-40% of maximal histamine stimulation at lower concentrations (10-7 and 10-6 M) and inhibition of histamine stimulation at higher concentrations (10-5 and 10-4 M). Histamine stimulated adenylate cyclase activity over the same dose range as that which produced a positive inotropic response in isolated papillary muscles. Under one set of assay conditions, contractile response and adenylate cyclase does-response curves were essentially super-imposable. We conclude that human myocardial adenylate cyclase is coupled to the H2 receptor and linked to the contractile response, whereas the H1 receptor does not mediate a biochemical or mechanical effect.

A simple technique was developed for the detection of intermediary metabolites of Aspergillus versicolor that are putative precursors of aflatoxin. Minicolony populations were allowed to metabolize [1,2-14C]acetate over various time intervals. The biosynthetic reactions were quenched by quick-freezing the minicolonies, the cells were disrupted, and the metabolites were extracted into acetone. Small silica thin-layer chromatographic plates were then used to separate any radioactive metabolites present. Elution in two or three different directions was often necessary. Radioautography of the thin-layer chromatography plates provided a sensitive assay for the appearance of the various intermediates in a timing pattern which implicated the sequence of formation. Transient intermediates were distinguished from dead-end metabolites by the rapid formation and disappearance of the former. At least five unknown precursors of versicolorin A, a dead-end metabolite, were recognized. The kinetic pulse-labeling technique should be generally applicable to other fungal species whenever the entrapment of intermediary metabolites in the mycelium poses and technical problem.

Desensitization of smooth muscle contraction was studied in aortic ring segments obtained from New England Deaconness Hospital rats harboring pheochromocytomas, a norepinephrine-secreting tumor. Rats were studied 5 to 6 weeks after implantation of the pheochromocytoma, by which time severe hypertension had developed. Aortic ring segments from the pheochromocytoma rats were significantly less sensitive to the alpha-1 adrenergic agonist phenylephrine [log10 (ED50) = -7.21 +/- 0.09 vs. -7.63 +/- 0.11 in controls). In addition, the maximal force of contraction induced by phenylephrine was decreased in the aortas from pheochromocytoma rats (1.31 +/- 0.15 g) compared to controls (2.17 +/- 0.23 g). The potency of the thromboxane A2 receptor agonist U-46,619 was decreased in the aortic ring segments from pheochromocytoma rats compared to controls, although it elicited a similar maximal force of contraction. Desensitization of alpha receptor-mediated contraction was prevented by treating the pheochromocytoma-bearing rats with the reversible alpha adrenergic antagonist phentolamine (200 micrograms/kg/hr) via osmotic minipumps for 2 weeks. However, phentolamine did not decrease the hypertension in these rats. Also, large doses of the irreversible alpha adrenergic antagonist phenoxybenzamine (4 mg/kg/day i.p.) did not decrease blood pressure in rats harboring pheochromocytoma or did the drug completely block aortic alpha receptors in these rats as it did in controls. The results indicate that pheochromocytoma induces heterologous desensitization of smooth muscle contraction in rat aorta. The desensitization is due to direct effects of catecholamines unrelated to hypertension. The New England Deaconess Hospital rat harboring pheochromocytoma is an interesting model to study the effects of high concentrations of plasma catecholamines on smooth muscle contraction.

New England Deaconness Hospital rats harboring a transplantable pheochromocytoma exhibit plasma norepinephrine concentrations 20-fold higher than controls. A cardiomyopathy (CM) characterized by multifocal areas of interstitial and replacement fibrosis, mixed inflammatory infiltrates and contraction band necrosis is evident 35 to 45 days after tumor implantation. Using a morphological scoring system of 0 (no cardiac damage) to 3 (involvement of almost the complete ventricular cross-section sampled), a CM score of 1.8 +/- 0.1 was found in rats harboring pheochromocytoma, a significant increase over that in age- and sex-matched controls (0.4 +/- 0.1, P less than .001). The pheochromocytoma rats also had hypertension (systolic blood pressure = 182 +/- 4 vs. 131 +/- 2 mm Hg in controls, P less than .001). In an effort to prevent the CM, rats harboring pheochromocytoma were treated with either the beta receptor antagonist timolol, the alpha receptor antagonists phentolamine or phenoxybenzamine or the nonspecific vasodilator hydralazine. Hydralazine normalized systolic blood pressure (135 +/- 6 mm Hg), whereas timolol (144 +/- 5 mm Hg), phenoxybenzamine (166 +/- 5 mm Hg) or phentolamine (154 +/- 10 mm Hg) only moderately decreased blood pressure in rats harboring pheochromocytoma. Hydralazine had no effect on CM score (1.8 +/- 0.1). Timolol markedly attenuated the CM score (0.6 +/- 0.1), whereas the alpha adrenergic antagonists were not as effective (phenoxybenzamine CM score = 1.3 +/- 0.2; phentolamine CM score = 1.7 +/- 0.2). Furthermore, timolol prevented desensitization of beta adrenergic receptor-mediated contraction in the hearts of rats harboring pheochromocytoma.(ABSTRACT TRUNCATED AT 250 WORDS)

We investigated the effects of clentiazem, a 1,5-benzothiazepine calcium antagonist, on epinephrine-induced cardiomyopathy in rats. With 2-week chronic epinephrine infusion, 16 of 30 rats died within 4 days, and severe ischemic lesions and fibrosis of the left ventricles were observed. In epinephrine-treated rats, left atrial and left ventricular papillary muscle contractile responses to isoproterenol were reduced, but responses to calcium were normal or enhanced compared to controls. Left ventricular alpha and beta adrenoceptor densities were also reduced compared to controls. Treatment with clentiazem prevented epinephrine-induced death (P < .05), and attenuated the ventricular ischemic lesions and fibrosis, in a dose-dependent manner. Left atrial and left ventricular papillary muscle contractile responses to isoproterenol were reduced compared to controls in groups treated with clentiazem alone, but combined with epinephrine, clentiazem restored left atrial responses and enhanced left ventricular papillary responses to isoproterenol. On the other hand clentiazem did not prevent epinephrine-induced down-regulation of alpha and beta adrenoceptors. Interestingly, clentiazem, infused alone, resulted in decreased adrenergic receptor densities in the left ventricle. Clentiazem also did not prevent the enhanced responses to calcium seen in the epinephrine-treated animals, although the high dose of clentiazem partially attenuated the maximal response to calcium compared to epinephrine-treated animals. In conclusion, clentiazem attenuated epinephrine-induced cardiac injury, possibly through its effect on the adrenergic pathway.